My vote for the most frustrating piece of crap that I have ever owned goes to Beseler and their MXIII enlarger. It is a dog to align and will stay in alignment for all of ten minutes. I also have a Beseler/Minolta 45 A lighthead with it. The 45A lighthead could use more power but in terms of repeatibility has been a wonderful device. The Beseler has been replaced with a Durst 445 that is over 30 years old and has been moved at least four times and its alignment is as good as the day it left the factory...SUPERB.
The worst piece of camera gear I have ever owned was an Alpa 6C. A beautiful, nicely finished camera with its wonderful Macro Switar lens had a terrible film advance system that was completely unreliable. After the fourth breakdown within one year ...approx. 1962... I wrote a nasty letter to the importer...Karl Heitz about how stupid I was to have paid more money for said camera than I would have paid for a Nikon F or a Leica M3... They sent me a new camera body. It was beautiful and it was broken within 2 weeks...Goodbye Alpa. Karl Heitz thought was a fine outfit with which to do business.